|Topic Review (Newest First)|
|01-05-2013 04:50 PM|
Your explanation has helped me to have a better understanding of why we bond underwater components.
This really is serious business & sure gives me something to think about.
|01-05-2013 03:10 PM|
Originally Posted by misfits View Post
Lots to consider. Under ABYC TE-4 it is suggested that you have primary and secondary lightning bonds. The main down conductor goes straight to the keel, unless encapsulated where you'd use an immersed ground strip, and this wire is as as straight as possible.
I personally diverge from TE-4 in the sheer size of the main down conductor and prefer at least 2/0 wire. I often opt for 2GA - 4GA for chainplates
For the seacocks, on bonded boats, fuel tank, rudder post, stuffing box etc. etc. I prefer to run all bonding directly back to the ships single main earth ground point, usually the engine. This gets the bonding wires for seacocks off the keel bolts and out of "direct line" strike duty and makes them more of a "secondary" lightning bond. I only wire the chainplates and mast straight to the keel bolts.
Originally Posted by misfits View Post
All metals have a voltage when immersed into an electrolyte. The current/voltage created by connecting all these dissimilar metals via the green earth ground wire can be damaging despite rarely if ever being over 1 volt. GI's ONLY block voltages below about 1.2V which is where galvanic corrosion activity is occurring thus they only protect against this one type of corrosion issue.
This type of corrosion is but one small piece of the corrosion puzzle. A lot of people assume a GI is the be all end all and it only serves ONE VERY SMALL portion of marine corrosion, blocking galvanic currents. They usually won't do much if anything for electrolytic corrosion or stray DC voltage leaks.
For example a hot bilge pump wire in the bilge of a boat, I see this all the time, that is not bonded, may eat the nearest seacock to it. Bond that same boat and you've now spread this current amongst all the under water metals and the voltage/current is much less damaging when divided by a much larger mass. You will hopefully notice the rapid zinc erosion and address the issue. Without bonding you can simply and easily eat that seacock and glug, glug, glug down goes the boat.
This happened recently and was written about by Ed Sherman the education director of the ABYC. An installer installed some bronze under water lights on a big expensive power boat (don't even get me going on the sheer stupidity of under water lighting).
Everything else on this boat was bonded but he did not bond the underwater bronze lights. The wire made contact with the bronze light fixture and ate it very rapidly until it simply fell out of the boat... The boat sunk in the slip. Had that light been bonded it would have been a much slower issue and the zinc erosion may have alerted the owner to a problem..
To bond or not to bond is not so simple and these are but two examples.....
I see a LOT MORE corrosion problems with moored boats than people would ever assume occur.
This DC corrosion occurred in less than 24 hours on a mooring. The owner changed the bilge pump switch and left a bare exposed connection because he used non heat shrink butt splices. This exposed 12V wire was in the skim coat of bilge water about 4" from this 12 week old seacock. It had recently been installed for a new bait well in the spring of that year.. The boat was not bonded thus the corrosion on this seacock was RAPID. This was the only seacock to suffer damage this bad. Another one about two feet away was also damaged but the closest one took the brunt.. If he had not caught this the boat would have sunk in another day or two.
People always assume marinas are the worst environment but the really bad corrosion issues, as in fast, aggressive metal eating corrosion (like above), is most often caused by your own boat and on-board DC leaks..
The only true "isolation" in a marina is to either unplug or use an isolation transformer.
|01-05-2013 02:38 PM|
Originally Posted by Maine Sail View Post
On my Sabre that we're renovating all the thru hull bonding connects to keel at the same point as the lightning bond. In another thread on this site & other publications say this is a bad thing to do. The bond wiring is in poor shape & needs to be replaced so....
In your opinion does it make sense to connect the bonding to the same point as the lightning system?
Does it make sense not to bond the thru hulls if an isolator is installed between the AC/DC grounds?
|01-05-2013 01:28 PM|
Thanks, Main. I'm going to scrub them clean as well. Now I have learned that Lanocote is available at WM and is a very useful marine product.
|01-05-2013 01:11 PM|
Originally Posted by rbrasi View Post
If your seacocks start to turn "pink" they you need to start worrying.. If you mixed yellow brass or any dissimilar metals in your seacock system then you can begin to worry. The most often "mixed" metal in a seacok system is when people try to cut corners on the male adapters and use Home Depot quality 60/40 yellow brass.
The thru-hull, seacock or ball valve body AND the male adapter or ANY nipples or elbows should all be of 85-5-5-5 bronze.
The green, in and of itself, is not a concern and is normal. It is what may be under the green that would be cause for concern. Green is ok but green can hide real corrosion so green can be bad if the seacocks are not cleaned and examined every now and then. Heck look at the bronze portlights of any older Cape Dory they are green with verdigris but are not submerged in an electrolyte.... If you want to minimize verdigris it slather a clean seacock with Lanocoat...
This is a good example of why articles like the WM Advisor/Honey article are so dangerous. We don't even understand the difference between a natural patina of bronze in a marine environment and what real corrosion looks like.
Below is a picture of dealloying or dezincification of brass. This is real corrosion and quite dangerous. Note the pink color to what used to be a goldish yellow piece of brass. This is why brass should not be used below waterline for seacocks, bonded or not. The "green" on this valve had nothing to do with this corrosion. The "zinc" content in the brass, upwards of 40%, clearly became the sacrificial metal to the 85-5-5-5 bronze thru-hull fitting or other more noble metals.
These were not bonded and if they were they would have likely survived better, in this particular application. Again, no one size fits all... When the wrench was put to this valve it literally crumbled because there was no zinc left in it. Proper 85-5-5-5 bronze seacocks are VERY, VERY, VERY resistant to dezincification. I have many customers with 40+ year old tapered cone 85-5-5-5 bronze seacocks in as good a condition, corrosion wise, as when they left the factory
|01-05-2013 12:42 PM|
Here is my rationale:
When I bought my boat, the thru hulls were bonded by the original owner. He owned the boat nearly 40 years and did everything right. It's become my rule of thumb on this ongoing project to just copy what the old guy did and I'll be fine. So, last year, a different guy who brokered the sale to me told me that bonding will not be necessary once we replaced the thru hulls (Groco). I went with that, and now 18 months later, I see that there is some green on a couple of the thru hulls. This tells me there is corrosion, so I bonded them yesterday. I will watch closely to see if anything changes. The question is, if they are correctly protected, then how long would it be before I begin to see the signs of corrosion? Also, since I am basically getting the boat ready for the next owner, I have to think in terms of what the surveyor will report. Maybe I should run this by a local who knows (Los Angeles).
|01-05-2013 10:39 AM|
Originally Posted by boatpoker View Post
The problem with this issue is that EVERY BOAT IS DIFFERENT!!!!!!!!!
Articles like the Stan Honey/WM Advisor article do a big disservice to the boating community, IMHO. That article over simplifies and leaves out a lot of pertinent information. I have actually had this very pointed conversation with Stan and he agreed that his article is very often interpreted incorrectly and people read what they want to read.
When it comes to things like lightning bonding, AC/DC Earth bond on-board, underwater metals bonding etc. etc. people tend to take only what they want to hear from an article without fully understanding the basis for any of the bond or not to bond arguments.
Our own vessels remains with the seacocks un-bonded, but, I have a bone dry bilge and our boat is impeccably wired compared to 99.5% of the boats out there.
Un-bonding the underwater metals on some vessels can cause major issues yet some boats can be un-bonded and not suffer issues or actually do better. This is why even the "experts" disagree on the topic of bonding. The only real truth is that YOUR BOAT should, at a bare minimum, undergo a full corrosion survey before making any of these changes.
Reading a "one pager" in the WM catalog does not even begin to scratch the surface of giving you even a baseline for understanding marine corrosion. I have yet to see a marina full of boats where a blanket "one size fits all" approach could be applied without in-depth analysis of each vessels electrical systems..
How many boat owners have, understand or use a Ag/AgCl reference cell? Hell, we can't even get people to install zincs correctly yet the WM Advisor is telling you to "unbond"....? Great.... Go for it......
Without a full corrosion survey I would strongly advise people not heed the overly simplistic advise of the WM article until you have a full grasp of what Stan was actually saying! Unless you have a full understanding of marine corrosion and have done a very, very thorough corrosion survey on your own vessel hold off on any changes until you have a better analysis of your vessel.... You may be very surprised at what you find.... You'd be horrified at what I find.....
|01-05-2013 09:52 AM|
Told ya !
If you are really interested in this and any other electric issues I highly recommend you visit Captain David Rifkin's website and look under "Documents". His website is a goldmine of clear and concise articles on marine electrical issues.
Dave is a retired nuclear sub commander, corrosion consultant to USCG and USN and one of the top guys in this field. I took one of his seminars a few weeks back and was greatly impressed.
|01-05-2013 09:33 AM|
Originally Posted by mitiempo View Post
What do you consider "isolated"? Does a rubber hose that connects a thru hull isolate it? If so what's the advantage of bonding or not bonding?
There's so many different opinions on this subject. A surveyor that I know & respect said in Europe it's common practice not to bond any thru hulls because they feel they're "isolated" when connected with a rubber hose. However when there's seawater sloshing around in the bilge the opportunity presents itself to "connect" all underwater thru hulls to the keel which is lead & the disimilar metal issue comes into play.
He also said he's for bonding providing all electrical connections are without corrosion so there's no resistence so everything is equal.
Personally I'm so confused about this subject I'm wondering if there is a right or wrong answer.
|01-05-2013 08:46 AM|
Originally Posted by Barrosa View Post
I have my own ideas about whether its a good or bad thing to do but I don't want to start a flame war
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